When it is desired to install branch tappings or parallel connections on pipes, such as gas distribution pipes, or indeed pipes for conveying other types of fluid, such as water, it is desirable, particularly in an urban environment, to be able to dig a hole of small dimensions so as to avoid disturbing the surroundings and so as to restrict the inconvenience caused to vehicle or pedestrian traffic. If the section of the trench is small, it is not possible for a person to go down to the bottom thereof, so the operations of installing the tapping must be capable of being performed from the top of the hole.
Proposals have already been made, in particular in documents FR-A-2 620 649 and FR-A-2 648 538 for various apparatuses that serve to put connection tappings into place on pipes, and in particular to exert clamping forces between a tapping and a pipe in order to facilitate welding the tapping to the pipe.
When the pipe and the parallel connection tapping are made of heat-fusible material, such as polyethylene, the tapping is advantageously secured to the pipe by welding. Under such circumstances, the saddle with which the parallel connection is provided is itself fitted with an electrical resistance element in the immediate proximity of its concave surface that is designed to be pressed against the convex surface of the pipe. While the tapping is held clamped against the pipe, electricity is caused to flow through the electrical resistance element of the saddle of the tapping, thereby causing the saddle of the tapping to melt and to be welded to the portion of the pipe that is in contact therewith.
In the prior art apparatuses described in the above-specified documents, a tapping is positioned by means of its own tubular column, and that does not make it possible to obtain an assembly of good quality and to guarantee a reliable weld. Unfortunately, with pipes such as gas mains, it is essential that the weld should avoid giving rise to faults that could subsequently give rise to gas leaks.
Furthermore, known positioning apparatuses are difficult to handle in the absence of abutment or guide elements, and they lend themselves poorly to use with tappings of various different types or with pipes of different diameters.